1. Field of the Invention
The present invention relates to an over voltage protection circuit and an electronic system, and more particularly, to an over voltage protection circuit and an electronic system capable of utilizing an upper gate switch and a lower gate switch of a motor driver or a fan driver (i.e. embedded driver-MOS IC in motor-driver application) to mitigate over voltage generated by a hot plug.
2. Description of the Prior Art
Most electronic devices (e.g. a fan, a display device) require a voltage provided by a power supply for operating regularly. When an electronic device is coupled to the power supply via a hot plug action, the power supply outputs a charging current according to the voltage generated by the power supply, for charging the electronic device. Then, a voltage regulating capacitor installed in the electronic device stores electric charges via the charging current, for increasing a voltage of the voltage regulating capacitor to a predefined high voltage, to provide a voltage required by the electronic device. However, for increasing the voltage of the voltage regulating capacitor to the predefined high voltage rapidly, the charging current outputted by the power supply is usually large and cannot be stopped immediately (due to characteristic of an inductance). Therefore, after the power supply starts to output the charging current, the voltage of the voltage regulating capacitor will be larger than the predefined high voltage during a period, and over voltage is caused in the period. The over voltage not only wastes electric power but reduces lifetime of the electronic device.
For example, please refer to FIG. 1, which is a schematic diagram of an electronic system 10 according to the prior art. The electronic system 10 includes a power supply PS, an inductance L_pa, a hot-plug port HP_port and an electronic device 100. Further, the electronic device 100 includes a voltage regulating capacitor C, a ground end VGD and a general loading 102, and is coupled to the power supply PS via the hot-plug port HP_port. Besides, the inductance L_pa is a parasitic inductance, and usually exists between the power supply PS and the electronic device 100. When the hot-plug port HP_port turns on, the power supply PS outputs a charging current I_ch according to a voltage V_ps generated by the power supply PS, for charging the voltage regulating capacitor C, such that a voltage V_in of the voltage regulating capacitor C increases to a predefined high voltage VCC. After the voltage V_in equals the predefined high voltage VCC, the power supply PS keeps the voltage V_ps constant, for stopping outputting the charging current I_ch, to stop the voltage V_in increasing. However, the inductance L_pa prevents the charging current I_ch from a sudden change. That is, the charging current I_ch continues to charge the voltage regulating capacitor C. Therefore, the voltage V_in continues to increase, and becomes larger than the predefined high voltage VCC and the over voltage is caused. In practice, when the predefined high voltage VCC is set to 12 volts and the inductance L_pa and the voltage regulating capacitor C with general specifications are used, the over voltage causes the voltage V_in to reach 30-40 volts which are greatly larger than the predefined high voltage VCC.
In detail, please refer to FIG. 2, which is a schematic diagram of variations of the voltage V_ps, the charging current I_ch and the voltage V_in shown in FIG. 1. When the hot-plug port HP_port turns on at time t1, the power supply PS increases the voltage V_ps immediately, and generates the charging current I_ch. Then, the voltage V_in starts to increase. When the voltage V_in increases to the predefined high voltage VCC at time t2, the inductance L_pa prevents the charging current I_ch from a sudden change, and the charging current I_ch continues to charge the voltage regulating capacitor C until time t3. When the charging current I_ch is zero and stops charging the voltage regulating capacitor C, the voltage V_in can discharge via the ground end VGD, to decrease to the predefined high voltage VCC at time t4. In other words, the general-loading 102 with a sink current will reduce the voltage V_in to the voltage V_ps. As shown in FIG. 2, the voltage V_in is affected by the over voltage between time t2 and time t4. Therefore, not only the electric power is wasted but the lifetime of the electronic device is reduced.
In the prior art, the voltage regulating capacitor C is increased for reducing an amplitude of increase of the voltage V_in, to mitigate the over voltage. However, it will still happen that the voltage V_in is larger than the predefined high voltage VCC. Besides, specification of the voltage regulating capacitor C is usually determined by a manufacturer of the electronic device but not an integrated circuit (IC) designer. That is, the method is restricted by features of the electronic device, and the over voltage cannot be solved completely. Therefore, how to solve the over voltage efficiently and completely is still a topic to be addressed.